Editing Sponge (section)

== Vital functions ==

[[File:Spongia officinalis.jpg|thumb|right|''[[Spongia officinalis]]'', "the kitchen sponge", is dark grey when alive.]]

=== Movement ===

Although adult sponges are fundamentally [[Sessility (zoology)|sessile]] animals, some marine and freshwater species can move across the sea bed at speeds of {{convert|1|-|4|mm|in|abbr=on}} per day, as a result of [[amoeba]]-like movements of [[pinacocyte]]s and other cells. A few species can contract their whole bodies, and many can close their [[osculum|oscula]] and [[wikt:ostium|ostia]]. Juveniles drift or swim freely, while adults are stationary.<ref name="Ruppert_2004"/>

=== Respiration, feeding and excretion ===

[[File:Venus Flower Basket.jpg|thumb|''[[Euplectella aspergillum]]'', a [[glass sponge]] known as "Venus's flower basket"]]

Sponges do not have distinct [[circulatory]], [[respiratory]], [[digestion|digestive]], and [[excretory]] systems – instead, the water flow system supports all these functions. They [[filter feeding|filter]] food particles out of the water flowing through them. Particles larger than 50&nbsp;micrometers cannot enter the [[wikt:ostium|ostia]] and [[pinacocyte]]s consume them by [[phagocytosis]] (engulfing and intracellular digestion). Particles from 0.5&nbsp;μm to 50&nbsp;μm are trapped in the ostia, which taper from the outer to inner ends. These particles are consumed by pinacocytes or by [[archaeocyte]]s which partially extrude themselves through the walls of the ostia. Bacteria-sized particles, below 0.5&nbsp;micrometers, pass through the ostia and are caught and consumed by [[choanocyte]]s.<ref name="Ruppert_2004"/> Since the smallest particles are by far the most common, choanocytes typically capture 80% of a sponge's food supply.<ref name="Bergquist_2001">{{cite book |contribution=Porifera (Sponges) |last=Bergquist |first=P.R. |title=Encyclopedia of Life Sciences |year=2001 |publisher= John Wiley & Sons |doi=10.1038/npg.els.0001582 |isbn=978-0-470-01617-6}}</ref> Archaeocytes transport food packaged in [[Vesicle (biology)|vesicles]] from cells that directly digest food to those that do not. At least one species of sponge has internal fibers that function as tracks for use by nutrient-carrying archaeocytes,<ref name="Ruppert_2004"/> and these tracks also move inert objects.<ref name="Bergquist_1998"/>

It used to be claimed that [[glass sponge]]s could live on nutrients dissolved in sea water and were very averse to silt.<ref name="Krautter_1998">{{cite journal |last=Krautter |first=M. |title=Ecology of siliceous sponges: Application to the environmental interpretation of the Upper Jurassic sponge facies (Oxfordian) from Spain |journal=[[Journal of Iberian Geology|Cuadernos de Geología Ibérica]] |pages=223–239 |year=1998 |volume=24 |url=http://www.ucm.es/BUCM/revistas/geo/16986180/articulos/JIGE9898110223A.PDF |archive-url=https://web.archive.org/web/20090319205858/http://www.ucm.es/BUCM/revistas/geo/16986180/articulos/JIGE9898110223A.PDF |archive-date=March 19, 2009 |access-date=2008-10-10 |url-status=dead }}</ref> However, a study in 2007 found no evidence of this and concluded that they extract bacteria and other micro-organisms from water very efficiently (about 79%) and process suspended sediment grains to extract such prey.<ref>{{cite journal |doi=10.4319/lo.2007.52.1.0428 |author1=Yahel, G. |author2=Whitney, F. |author3=Reiswig, H.M. |author4=Eerkes-Medrano, D.I. |author5=Leys, S.P. |year=2007 |title=In situ feeding and metabolism of glass sponges (Hexactinellida, Porifera) studied in a deep temperate fjord with a remotely operated submersible |journal=[[Limnology and Oceanography]] |volume=52|issue=1|pages=428–440|citeseerx=10.1.1.597.9627|bibcode=2007LimOc..52..428Y|s2cid=86297053 }}</ref> Collar bodies digest food and distribute it wrapped in vesicles that are transported by [[dynein]] "motor" molecules along bundles of [[microtubule]]s that run throughout the [[syncytium]].<ref name="Ruppert_2004"/>

Sponges' cells absorb oxygen by [[diffusion]] from water into cells as water flows through body, into which [[carbon dioxide]] and other soluble waste products such as [[ammonia]] also diffuse. Archeocytes remove mineral particles that threaten to block the ostia, transport them through the mesohyl and generally dump them into the outgoing water current, although some species incorporate them into their skeletons.<ref name="Ruppert_2004"/>

=== Carnivorous sponges ===

[[File:Chondrocladia lampadiglobus.jpg|thumb|The carnivorous ping-pong tree sponge, ''[[Chondrocladia]] lampadiglobus''<ref>{{cite journal |last1=Van Soest |first1=Rob W. M. |last2=Boury-Esnault |first2=Nicole |last3=Vacelet |first3=Jean |last4=Dohrmann |first4=Martin |last5=Erpenbeck |first5=Dirk |last6=De Voogd |first6=Nicole J. |last7=Santodomingo |first7=Nadiezhda |last8=Vanhoorne |first8=Bart |last9=Kelly |first9=Michelle |last10=Hooper |first10=John N. A. |title=Global diversity of sponges (Porifera) |journal=PLOS ONE |volume=7 |issue=4 |pages=e35105 |year=2012 |pmid=22558119 |pmc=3338747 |doi=10.1371/journal.pone.0035105 |doi-access=free |bibcode=2012PLoSO...735105V |author-link9=Michelle Kelly (marine scientist) }}</ref>]]

In waters where the supply of food particles is very poor, some species prey on [[crustacea]]ns and other small animals. As of 2014, a total of 137 species had been discovered.<ref>{{cite news|date=April 19, 2014 |url=http://www.cbc.ca/news/canada/british-columbia/4-new-species-of-killer-sponges-discovered-off-pacific-coast-1.2615509 |title=4 new species of 'killer' sponges discovered off Pacific coast |work=[[CBC News]] |access-date=2014-09-04 |url-status=live |archive-url=https://web.archive.org/web/20140419143139/http://www.cbc.ca/news/canada/british-columbia/4-new-species-of-killer-sponges-discovered-off-pacific-coast-1.2615509 |archive-date=April 19, 2014 }}</ref> Most belong to the [[family (biology)|family]] [[Cladorhizidae]], but a few members of the [[Guitarridae]] and [[Esperiopsidae]] are also carnivores.<ref name="Vacelet_2008"/> In most cases, little is known about how they actually capture prey, although some species are thought to use either sticky threads or hooked [[sponge spicule|spicules]].<ref name="Vacelet_2008"/><ref>{{cite journal|last= Watling |first=L. |title=Predation on copepods by an Alaskan cladorhizid sponge |journal=[[Journal of the Marine Biological Association of the United Kingdom]] |year= 2007|volume=87 |pages=1721–1726 |doi=10.1017/S0025315407058560|issue=6 |bibcode=2007JMBUK..87.1721W |s2cid=86588792}}</ref> Most carnivorous sponges live in deep waters, up to {{convert|8840|m|mi|abbr=on}},<ref name="Vacelet_1995">{{cite journal |last1= Vacelet |first1=J. |last2=Boury-Esnault |first2=N. |title=Carnivorous sponges|journal=Nature|volume=373|pages=333–335|year=1995|doi=10.1038/373333a0|issue=6512|bibcode=1995Natur.373..333V|s2cid=4320216|doi-access=free}}</ref> and the development of deep-ocean exploration techniques is expected to lead to the discovery of several more.<ref name="Ruppert_2004"/><ref name="Vacelet_2008">{{cite journal |last1=Vacelet |first1=J. |title=A new genus of carnivorous sponges (Porifera: Poecilosclerida, Cladorhizidae) from the deep N-E Pacific, and remarks on the genus ''Neocladia''|journal=[[Zootaxa]]|url=http://www.mapress.com/zootaxa/2008/f/z01752p065f.pdf |archive-url=https://web.archive.org/web/20080906190452/http://www.mapress.com/zootaxa/2008/f/z01752p065f.pdf |archive-date=2008-09-06 |url-status=live|volume=1752|pages=57–65|year=2008|access-date=2008-10-31|doi=10.11646/zootaxa.1752.1.3}}</ref> However, one species has been found in [[Mediterranean]] caves at depths of {{convert|17|-|23|m|ft|abbr=on}}, alongside the more usual [[filter-feeding]] sponges. The cave-dwelling predators capture crustaceans under {{convert|1|mm|in|abbr=on}} long by entangling them with fine threads, digest them by enveloping them with further threads over the course of a few days, and then return to their normal shape; there is no evidence that they use [[venom]].<ref name="Vacelet_1995"/>

Most known carnivorous sponges have completely lost the water flow system and [[choanocyte]]s. However, the [[genus]] ''[[Chondrocladia]]'' uses a highly modified water flow system to inflate balloon-like structures that are used for capturing prey.<ref name="Vacelet_2008"/><ref name="Vacele_2008">{{cite journal |last1= Vacelet |first1=J. |last2=Kelly |first2=Michelle |author-link2=Michelle Kelly (marine scientist) |title=New species from the deep Pacific suggest that carnivorous sponges date back to the Early Jurassic|journal=Nature Precedings|year=2008|doi= 10.1038/npre.2008.2327.1|doi-access=free}}</ref>

=== Endosymbionts ===

Freshwater sponges often host [[green algae]] as [[endosymbiont]]s within [[archaeocyte]]s and other cells and benefit from nutrients produced by the algae. Many marine species host other [[photosynthesis|photosynthesizing]] organisms, most commonly [[cyanobacteria]] but in some cases [[dinoflagellate]]s. Symbiotic cyanobacteria may form a third of the total mass of living tissue in some sponges, and some sponges gain 48% to 80% of their energy supply from these micro-organisms.<ref name="Ruppert_2004"/> In 2008, a [[University of Stuttgart]] team reported that spicules made of [[silica]] conduct light into the [[mesohyl]], where the photosynthesizing endosymbionts live.<ref>{{cite journal |last1=Brümmer |first1=Franz |last2=Pfannkuchen |first2=Martin |last3=Baltz |first3=Alexander |last4=Hauser |first4=Thomas |last5=Thiel |first5=Vera |title=Light inside sponges |journal=[[Journal of Experimental Marine Biology and Ecology]] |volume=367 |issue=2 |pages=61–64 |doi=10.1016/j.jembe.2008.06.036 |year=2008|bibcode=2008JEMBE.367...61B }}
* {{cite news |last=Walker |first=Matt |date=10 November 2008 |title=Nature's 'fibre optics' experts |work=BBC News |url=http://news.bbc.co.uk/2/hi/science/nature/7720836.stm |access-date=11 November 2008 |archive-date=17 December 2008 |archive-url=https://web.archive.org/web/20081217045607/http://news.bbc.co.uk/2/hi/science/nature/7720836.stm |url-status=live }}</ref> Sponges that host photosynthesizing organisms are most common in waters with relatively poor supplies of food particles and often have leafy shapes that maximize the amount of sunlight they collect.<ref name="Bergquist_1998"/>

A recently discovered carnivorous sponge that lives near [[hydrothermal vent]]s hosts [[Methanotrophic|methane-eating]] bacteria and digests some of them.<ref name="Bergquist_1998"/>

=== "Immune" system ===

Sponges do not have the complex [[immune system]]s of most other animals. However, they reject [[Medical grafting|grafts]] from other species but accept them from other members of their own species. In a few marine species, gray cells play the leading role in rejection of foreign material. When invaded, they produce a chemical that stops movement of other cells in the affected area, thus preventing the intruder from using the sponge's internal transport systems. If the intrusion persists, the grey cells concentrate in the area and release toxins that kill all cells in the area. The "immune" system can stay in this activated state for up to three weeks.<ref name="Bergquist_1998"/>

=== Reproduction ===

==== Asexual ====

[[File:Spongilla lacustris.jpg|thumb|right|The freshwater sponge ''[[Spongilla lacustris]]'']]

Sponges have three [[asexual reproduction|asexual]] methods of reproduction: after fragmentation, by [[budding]], and by producing [[gemmule]]s. Fragments of sponges may be detached by currents or waves. They use the mobility of their [[pinacocyte]]s and [[choanocyte]]s and reshaping of the [[mesohyl]] to re-attach themselves to a suitable surface and then rebuild themselves as small but functional sponges over the course of several days. The same capabilities enable sponges that have been squeezed through a fine cloth to regenerate.<ref name="Ruppert_2004"/>{{rp|239}} A sponge fragment can only regenerate if it contains both [[collencyte]]s to produce [[mesohyl]] and [[archeocyte]]s to produce all the other cell types.<ref name="Bergquist_2001"/> A very few species reproduce by budding.<ref name="Ruppert_2004"/>{{rp|90–94}}

Gemmules are "survival pods" which a few marine sponges and many freshwater species produce by the thousands when dying and which some, mainly freshwater species, regularly produce in autumn. [[Spongocyte]]s make gemmules by wrapping shells of spongin, often reinforced with spicules, round clusters of [[archeocyte]]s that are full of nutrients.<ref name="Ruppert_2004"/>{{rp|87–88}} Freshwater gemmules may also include photosynthesizing symbionts.<ref name="Smith_2001">{{cite book|author1=Smith, D. G. |author2=Pennak, R. W. |title=Pennak's Freshwater Invertebrates of the United States: Porifera to Crustacea |publisher=[[John Wiley and Sons]]|year=2001 |isbn=978-0-471-35837-4 |pages=47–50 |edition=4 |url={{google books|plainurl=y|id=GqIctb8IqPoC|page=48}}}}</ref> The gemmules then become dormant, and in this state can survive cold, drying out, lack of oxygen and extreme variations in [[salinity]].<ref name="Ruppert_2004"/> Freshwater gemmules often do not revive until the temperature drops, stays cold for a few months and then reaches a near-"normal" level.<ref name="Smith_2001"/> When a gemmule germinates, the archeocytes round the outside of the cluster transform into [[pinacocyte]]s, a membrane over a pore in the shell bursts, the cluster of cells slowly emerges, and most of the remaining archeocytes transform into other cell types needed to make a functioning sponge. Gemmules from the same species but different individuals can join forces to form one sponge.<ref name="Ruppert_2004"/>{{rp|89–90}} Some gemmules are retained within the parent sponge, and in spring it can be difficult to tell whether an old sponge has revived or been "recolonized" by its own gemmules.<ref name="Smith_2001"/>

==== Sexual ====

Most sponges are [[hermaphrodite]]s (function as both sexes simultaneously), although sponges have no [[gonad]]s (reproductive organs). Sperm are produced by [[choanocyte]]s or entire choanocyte chambers that sink into the [[mesohyl]] and form spermatic [[cyst]]s while eggs are formed by transformation of [[archeocyte]]s, or of choanocytes in some species. Each egg generally acquires a [[yolk]] by consuming "nurse cells". During spawning, sperm burst out of their cysts and are expelled via the [[osculum]]. If they contact another sponge of the same species, the water flow carries them to choanocytes that engulf them but, instead of digesting them, metamorphose to an [[ameboid]] form and carry the sperm through the mesohyl to eggs, which in most cases engulf the carrier and its cargo.<ref name="Ruppert_2004"/>{{rp|77}}

A few species release fertilized eggs into the water, but most retain the eggs until they hatch. By retaining the eggs, the parents can transfer symbiotic microorganisms directly to their offspring through [[vertical transmission]], while the species who release their eggs into the water has to acquire symbionts horizontally (a combination of both is probably most common, where larvae with vertically transmitted symbionts also acquire others horizontally).<ref>{{cite journal |last1=Díez-Vives |first1=Cristina |last2=Koutsouveli |first2=Vasiliki |last3=Conejero |first3=Maria |last4=Riesgo |first4=Ana |title=Global patterns in symbiont selection and transmission strategies in sponges |journal=Frontiers in Ecology and Evolution |volume=10 |date=26 October 2022 |issn=2296-701X |doi=10.3389/fevo.2022.1015592 |doi-access=free}}</ref><ref>{{cite journal |last1=Carrier |first1=Tyler J. |last2=Maldonado |first2=Manuel |last3=Schmittmann |first3=Lara |last4=Pita |first4=Lucía |last5=Bosch |first5=Thomas C. G. |last6=Hentschel |first6=Ute |title=Symbiont transmission in marine sponges: reproduction, development, and metamorphosis |journal=BMC Biology |volume=20 |issue=1 |pages=100 |date=May 2022 |pmid=35524305 |pmc=9077847 |doi=10.1186/s12915-022-01291-6 |doi-access=free }}</ref> There are four types of larvae, but all are lecithotrophic (non-feeding) balls of cells with an outer layer of cells whose [[flagella]] or [[cilia]] enable the larvae to move. After swimming for a few days the larvae sink and crawl until they find a place to settle. Most of the cells transform into archeocytes and then into the types appropriate for their locations in a miniature adult sponge.<ref name="Ruppert_2004"/>{{rp|77}}<ref>{{cite journal |last1=Riesgo |first1=Ana |last2=Taboada |first2=Sergio |last3=Sánchez-Vila |first3=Laura |last4=Solà |first4=Joan |last5=Bertran |first5=Andrea |last6=Avila |first6=Conxita |title=Some Like It Fat: Comparative Ultrastructure of the Embryo in Two Demosponges of the Genus Mycale (Order Poecilosclerida) from Antarctica and the Caribbean |journal=PLOS ONE |volume=10 |issue=3 |date=18 March 2015 |issn=1932-6203 |pmid=25785444 |pmc=4365022 |doi=10.1371/journal.pone.0118805 |doi-access=free |page=e0118805|bibcode=2015PLoSO..1018805R }}</ref>

[[Glass sponge]] embryos start by dividing into separate cells, but once 32&nbsp;cells have formed they rapidly transform into larvae that externally are [[ovoid]] with a band of [[cilia]] round the middle that they use for movement, but internally have the typical glass sponge structure of spicules with a cobweb-like main [[syncitium]] draped around and between them and [[choanosyncytia]] with multiple collar bodies in the center. The larvae then leave their parents' bodies.<ref>{{cite journal |last=Leys |first=S. P. |title=Embryogenesis in the glass sponge Oopsacas minuta: Formation of syncytia by fusion of blastomeres |journal=Integrative and Comparative Biology |volume=46 |issue=2 |date=16 February 2006 |issn=1540-7063 |doi=10.1093/icb/icj016 |pages=104–117|pmid=21672727 }}</ref>

===Meiosis===

The cytological progression of porifera [[oogenesis]] and [[spermatogenesis]] ([[gametogenesis]]) is very similar to that of other metazoa.<ref name="Koutsouveli_2020">{{cite journal |last1=Koutsouveli |first1=Vasiliki |last2=Cárdenas |first2=Paco |last3=Santodomingo |first3=Nadiezhda |last4=Marina |first4=Anabel |last5=Morato |first5=Esperanza |last6=Rapp |first6=Hans Tore |last7=Riesgo |first7=Ana |title=The Molecular Machinery of Gametogenesis in Geodia Demosponges (Porifera): Evolutionary Origins of a Conserved Toolkit across Animals |journal=Molecular Biology and Evolution |volume=37 |issue=12 |date=16 December 2020 |issn=0737-4038 |pmid=32929503 |pmc=7743902 |doi=10.1093/molbev/msaa183 |pages=3485–3506}}</ref> Most of the genes from the classic set of [[meiosis|meiotic]] genes, including genes for DNA recombination and double-strand break repair, that are conserved in [[eukaryote]]s are expressed in the sponges (e.g. ''[[Geodia hentscheli]]'' and ''Geodia phlegraei'').<ref name="Koutsouveli_2020"/> Since porifera are considered to be the earliest divergent animals, these findings indicate that the basic toolkit of meiosis including capabilities for recombination and DNA repair were present early in eukaryote evolution.<ref name="Koutsouveli_2020"/>

==== Life cycle ====
[[File:Bathymetrical range of selected sponge species.jpg|thumb|upright=1.5|right|Bathymetrical range of some sponge species.<ref>{{cite journal |last=Łukowiak |first=M. |title=Utilizing sponge spicules in taxonomic, ecological and environmental reconstructions: a review |journal=PeerJ |volume=8 |pages=e10601 |date=18 December 2020 |pmid=33384908 |pmc=7751429 |doi=10.7717/peerj.10601 |doi-access=free }}</ref> Demosponge ''[[Samus anonymus]]'' (up to 50&nbsp;m), [[hexactinellid]] ''Scleroplegma lanterna'' (~100–600&nbsp;m), hexactinellid ''Aulocalyx irregularis'' (~550–915&nbsp;m), lithistid demosponge ''Neoaulaxinia persicum'' (~500–1700&nbsp;m)]]

Sponges in [[temperate]] regions live for at most a few years, but some [[Tropics|tropical]] species and perhaps some deep-ocean ones may live for 200&nbsp;years or more. Some calcified [[demosponge]]s grow by only {{convert|0.2|mm|in|abbr=on}} per year and, if that rate is constant, specimens {{convert|1|m|ft|abbr=on}} wide must be about 5,000&nbsp;years old. Some sponges start sexual reproduction when only a few weeks old, while others wait until they are several years old.<ref name="Ruppert_2004"/>

=== Coordination of activities ===

Adult sponges lack [[neuron]]s or any other kind of [[nervous tissue]]. However, most species have the ability to perform movements that are coordinated all over their bodies, mainly contractions of the [[pinacocyte]]s, squeezing the water channels and thus expelling excess sediment and other substances that may cause blockages. Some species can contract the [[osculum]] independently of the rest of the body. Sponges may also contract in order to reduce the area that is vulnerable to attack by predators. In cases where two sponges are fused, for example if there is a large but still unseparated bud, these contraction waves slowly become coordinated in both of the "[[Siamese twins]]". The coordinating mechanism is unknown, but may involve chemicals similar to [[neurotransmitter]]s.<ref>{{cite journal |last=Nickel |first=M. |title=Kinetics and rhythm of body contractions in the sponge Tethya wilhelma (Porifera: Demospongiae) |journal=The Journal of Experimental Biology |volume=207 |issue=Pt 26 |pages=4515–24 |date=December 2004 |pmid=15579547 |doi=10.1242/jeb.01289 |doi-access=free |bibcode=2004JExpB.207.4515N }}</ref> However, [[glass sponge]]s rapidly transmit electrical impulses through all parts of the [[syncytium]], and use this to halt the motion of their [[flagella]] if the incoming water contains toxins or excessive sediment.<ref name="Ruppert_2004"/> [[Myocyte]]s are thought to be responsible for closing the osculum and for transmitting signals between different parts of the body.<ref name="Bergquist_1998"/>

Sponges contain [[gene]]s very similar to those that contain the "recipe" for the post-[[synapse|synaptic]] density, an important signal-receiving structure in the neurons of all other animals. However, in sponges these genes are only activated in "flask cells" that appear only in larvae and may provide some sensory capability while the larvae are swimming. This raises questions about whether flask cells represent the predecessors of true neurons or are evidence that sponges' ancestors had true neurons but lost them as they adapted to a sessile lifestyle.<ref>{{cite journal |last1=Sakarya |first1=Onur |last2=Armstrong |first2=Kathryn A. |last3=Adamska |first3=Maja |last4=Adamski |first4=Marcin |last5=Wang |first5=I-Fan |last6=Tidor |first6=Bruce |last7=Degnan |first7=Bernard M. |last8=Oakley |first8=Todd H. |last9=Kosik |first9=Kenneth S. |title=A Post-Synaptic Scaffold at the Origin of the Animal Kingdom |journal=PLOS ONE |volume=2 |issue=6 |date=6 June 2007 |issn=1932-6203 |pmid=17551586 |pmc=1876816 |doi=10.1371/journal.pone.0000506 |doi-access=free |page=e506|bibcode=2007PLoSO...2..506S }}</ref>
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Sponges have several cell types:
* [[Archaeocytes]] (or [[amoebocytes]]) have many functions; they are [[totipotent]] cells which can transform into [[sclerocytes]], [[spongocytes]], or [[collencytes]]. They also have a role in nutrient transport and sexual reproduction.
* Cells are arranged in a gelatinous non-cellular [[Matrix (biology)|matrix]] called mesohyll
Sponges have three body types: [[asconoid]], [[syconoid]], and [[leuconoid]].
* [[Choanocyte]]s (also known as "collar cells") function as the sponge's [[digestive system]], and are remarkably similar to the [[protist]]an [[choanoflagellate]]s. The collars are composed of many [[Microvillus|microvilli]] and are used to filter particles out of the water. The beating of the choanocytes' [[flagellum|flagella]] creates the sponge's water current.
* [[Collencytes]] secrete [[collagen]].
* [[Myocytes (sponge)|Myocytes]] are modified pinacocytes which control the size of the osculum and pore openings and thus the water flow.
* [[Pinacocytes]] which form the [[pinacoderm]], the outer epidermal layer of cells. This is the closest approach to true tissue in sponges
* [[Porocytes]] are tubular cells that make up the sponge's pores.
* [[Sclerocytes]] secrete [[calcareous]] siliceous spicules which reside in the mesohyl.
* [[Spongocytes]] secrete [[spongin]], [[collagen]]-like fibers which make up the mesohyl.
* [[Sponge spicule|Spicules]] are stiffened rods or spikes made of [[calcium carbonate]] or [[Silicon dioxide|silica]] which are used for structure and [[antipredator adaptation|defense]].
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